While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry's future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of α-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics.
Single-site olefin polymerization catalysts having “open architecture” are generally known. Examples include the so-called “constrained geometry” catalysts developed by scientists at Dow Chemical Company (see, e.g., U.S. Pat. No. 5,064,802), which have been used to produce a variety of polyolefins. “Open architecture” catalysts differ structurally from ordinary bridged metallocenes, which have a bridged pair of pi-electron donors. In open architecture catalysts, only one group of the bridged ligand donates pi electrons to the metal; the other group is sigma bonded to the metal. An advantage of this type of bridging is thought to be a more open or exposed locus for olefin complexation and chain propagation when the complex becomes catalytically active. Simple examples of complexes with open architecture are tert-butylamido(cyclopentadienyl)dimethylsilylzirconium dichloride and methylamido(cyclopentadienyl)-1,2-ethanediyltitanium dimethyl: 
Organometallic complexes that incorporate “indenoindolyl” ligands are known (see U.S. Pat. Nos. 6,232,260 and 6,451,724). The '260 patent demonstrates the use of non-bridged bis(indenoindolyl) complexes for making HDPE in a slurry polymerization. Versatility is an advantage of the complexes; by modifying the starting materials, a wide variety of indenoindolyl complexes can be prepared. “Open architecture” complexes are neither prepared nor specifically discussed. The '724 patent (“Nifant'ev”) teaches the use of bridged indenoindolyl complexes as catalysts for making polyolefins, including polypropylene, HDPE and LLDPE. The complexes disclosed by Nifant'ev do not have open architecture.
PCT Int. Appl. WO 01/53360 (Resconi et al.) discloses bridged indenoindolyl complexes having open architecture and their use to produce substantially amorphous propylene-based polymers. U.S. Pat. No. 6,559,251 discloses a process to make low density ethylene copolymers with catalysts having a bridged indenoindolyl ligand with open architecture. Copending application Ser. No. 10/382,233 discloses that indeno[1,2-b]indolyl catalysts provide exceptional activities in the preparation of elastomeric polypropylene and ethylene copolymers.
While the use of indenoindolyl complexes with open architecture is known, the use of additives to improve molecular weight is not. In particular, the use of hydrosilanes has not been contemplated.
The incorporation of silanes in polymerizations using cyclopentadienyl metallocene catalysts is described in EP 0739910, J. Am. Chem. Soc. 121 (1999) 8791 and in U.S. Pat. Nos. 5,578,690, 6,075,103 and 6,077,919. High levels of silane are used to lower the molecular weight. For instance, in the seventeen examples of EP 0739910, the silane is used in amounts of 26,800 to 465,000 ppm Si. At these levels, polymer molecular weight decreases with increasing silane and there is no clear effect on activity.
U.S. Pat. No. 6.642.326 uses low levels of hydrosilanes with boraaryl single-site catalyst precursors. It teaches an improvement in activity at low levels and that at higher hydrosilane levels, the polyolefin molecular weight can be undesirably low. In their polymerization examples with low levels of hydrosilanes, there is no indication of increased molecular weight. Where molecular weight is reported, it is lower than the control in three of the four instances.
While there has been no study of the use of hydrosilanes with indenoindolyl catalysts, analogy with other single-site catalyst systems would indicate that any effect would be to lower polyolefin molecular weight.
As noted earlier, the indenoindolyl framework is versatile. The need continues, however, for new ways to make polyolefins with increased molecular weight. Molecular weight affects several properties such as impact and toughness. For certain applications, high molecular weight polyolefins are required. The industry would also benefit from the availability of new processes that capitalize on the inherent flexibility of the indenoindolyl framework.